1. Field of the Invention
The present invention relates to cable television generally and more particularly to a two-way (interactive) cable-television system having distributed processing and means for regulating the upstream signal flow.
2. Description of the Prior Art
Cable television, also referred to as community antenna television (CATV), has come a long way from its humble beginning as a means of providing rural television reception. Presently, cable television is an important means of providing reception of local, non-local and premium television programs and promises to become an important means of providing many new, two-way (interactive) services in the future. Heretofore, cable television also promised a number of problems.
One such problem, even for one-way cable-television systems, is that of signal security. Many prior-art one-way cable-television systems transmit signals conveying premium television programs only to those who have made arrangements in advance (paid) for such programs. To restrict the reception of such programs, the signals conveying the programs are scrambled and those who have made arrangements to receive the programs are provided suitable descramblers. Unfortunately, such descramblers are relatively expensive. Further, it is difficult to securely scramble television signals, the redundant information in the signals making the signals relatively easy to descramble. Even for those who lack the requisite skills to build descramblers, such devices can often be purchased. For many two-way services, such as electronic mail, the signal security problem is evern more acute.
Another problem for two-way cable-television systems is that of noise. Noise, which typically enters at the drop cable level, must be prevented from propagating up the system (upstream) to disable the entire system.
A very serious problem is that of system loading. It is difficult to provide highly interactive services to a relatively large number of subscribers without so loading down prior-art-type two-way cable-television systems that the response time (delay) during peak hours becomes intolerable.
An interactive (two-way) cable-television system is disclosed in the U.S. Pat. No. 3,997,718 which issued to Ricketts et al. Disclosed is an interactive cable-television system employing a head-end subsystem, a plurality of subscriber units and a coaxial cable subsystem which interconnects the head-end subsystem with the various subscriber units. The system is operative to distribute television signals to the various subscriber units and to provide two-way digital data communications between the head-end subsystem and the various subscriber units. An encoder is employed in the head-end subsystem; and, a decoder is employed in each of the subscriber units, the combination for scrambling/descrambling premium television signals to restrict the use thereof. Also employed is a mini-computer in the head-end subsystem and the combination of an alpha-numeric keyboard with alpha-numeric electronics in each of the subscriber units to operate with a subscriber's television as a data terminal for two-way digital data communications with the mini-computer. Two-way digital data communication is carried on synchronously with each subscriber unit being allocated a time slot in which to respond. Another system employing many of the same elements is disclosed in the U.S. Pat. No. 4,245,245 issued to Matsumoto et al.
A two-way cable-television system is disclosed in U.S. Pat. No. 3,750,022 which issued to Curry et al. Employed therein is a tree-type distribution subsystem having nodally disposed filters. Each of the filters responds to respective head-end subsystem generated commands to isolate noise developed on a respective coaxial cable (drop cable) leading to a corresponding subscriber unit(s).
Another two-way cable-television system employing a tree-type distribution network is disclosed in the U.S. Pat. No. 3,840,812 which issued to T. Takeuchi. The system employs a number of nodally disposed modulation units each for modulation by an alarm signal generated by one of a number of associated subscriber alarm transmitters. Not only does each of the modulation units operates upon a distinct carrier frequency; but, each of the alarm transmitters associated therewith also operates upon a distinct audio frequency. This permits a head-end subsystem to identify the origin of an alarm signal. The nodally disposed modulation units operate upon the alarm signals so as to permit a much larger number of subscriber transmitters to share the distribution network than would otherwise be possible.
Finally, a two-way cable-television system is disclosed by A. Bernhart in the U.S. Pat. No. 3,934,079 in which it is indicated that two-way digital communication is by means of synchronously generated data packets.
A data communication (time share) network is disclosed in the U.S. Pat. No. 4,156,798 issued to M. Doelz. The network employs a number of host processing systems each coupled by a communications network to a number of terminal devices. Each of the processing systems is interconnected with the other processing systems to share data. The communications network includes a plurality of two-part buffer storage memories, fan-out node devices, line-master exchange unit devices, line exchange unit devices, and terminal exchange unit devices, all connected in a complex tree-ring configuration. Communication between the host processing system and a terminal device is by means of data blocks, erroneous blocks being discarded by the respective terminal exchange unit.
Television-type infra-red remote control units are disclosed in the U.S. Pat. Nos. 4,231,031 and 4,156,810, which issued to Crother et al and S. Igarashi, respectively. Both units employ infra-red radiation. Crother et al disclose the use of infra-red pulse spacing to represent each bit of digital data. In the S. Igarashi disclosure, the infra-red pulse spacing represents a digital quantity (word), in this case the desired channel number.